app2.rb

class FIFO
  def initialize
    @buffer = ''
    @eol = "\n"
  end

  def <<(chunk)
    @buffer << chunk
  end

  def next_line
    idx = @buffer.index(@eol)
    @buffer.slice!(0, idx + 1) unless idx.nil?
  end

  def next_line2
    idx = @buffer.index(@eol)

    unless idx.nil?
      @buffer.freeze
      rbuf = @buffer.slice(0, idx + 1)
      @buffer = @buffer.slice(idx + 1, @buffer.size)
      rbuf
    end
  end
end

log = "this is a log\n".freeze

f1 = FIFO.new

N = 5
N.times do
  f1 << log
end
require 'memory_profiler'
size = 0

if ENV["SLICE_BANG"]
  report = MemoryProfiler.report do
    N.times do
      size += f1.next_line.size
    end
  end
else
  report = MemoryProfiler.report do
    N.times do
      size += f1.next_line2.size
    end
  end
end

report.pretty_print
p size

Gemfile

# frozen_string_literal: true

source "https://rubygems.org"

git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }

gem "benchmark-memory"

result1.md

slice! version

$ SLICE_BANG=be ruby app2.rb                                                                                                  
Total allocated: 716 bytes (13 objects)
Total retained:  0 bytes (0 objects)

allocated memory by gem
-----------------------------------
       716  other

allocated memory by file
-----------------------------------
       716  app2.rb

allocated memory by location
-----------------------------------
       716  app2.rb:13

allocated memory by class
-----------------------------------
       716  String

allocated objects by gem
-----------------------------------
        13  other

allocated objects by file
-----------------------------------
        13  app2.rb

allocated objects by location
-----------------------------------
        13  app2.rb:13

allocated objects by class
-----------------------------------
        13  String

retained memory by gem
-----------------------------------
NO DATA

retained memory by file
-----------------------------------
NO DATA

retained memory by location
-----------------------------------
NO DATA

retained memory by class
-----------------------------------
NO DATA

retained objects by gem
-----------------------------------
NO DATA

retained objects by file
-----------------------------------
NO DATA

retained objects by location
-----------------------------------
NO DATA

retained objects by class
-----------------------------------
NO DATA


Allocated String Report
-----------------------------------
         5  ""
         5  app2.rb:13

         5  "this is a log\n"
         5  app2.rb:13

         1  "this is a log\nthis is a log\nthis is a log\n"
         1  app2.rb:13

         1  "this is a log\nthis is a log\nthis is a log\nthis is a log\n"
         1  app2.rb:13

         1  "this is a log\nthis is a log\nthis is a log\nthis is a log\nthis is a log\n"
         1  app2.rb:13

70

slice + freeze version

$ ruby app2.rb                                                                                                                
Total allocated: 400 bytes (10 objects)
Total retained:  40 bytes (1 objects)

allocated memory by gem
-----------------------------------
       400  other

allocated memory by file
-----------------------------------
       400  app2.rb

allocated memory by location
-----------------------------------
       200  app2.rb:21
       200  app2.rb:22

allocated memory by class
-----------------------------------
       400  String

allocated objects by gem
-----------------------------------
        10  other

allocated objects by file
-----------------------------------
        10  app2.rb

allocated objects by location
-----------------------------------
         5  app2.rb:21
         5  app2.rb:22

allocated objects by class
-----------------------------------
        10  String

retained memory by gem
-----------------------------------
        40  other

retained memory by file
-----------------------------------
        40  app2.rb

retained memory by location
-----------------------------------
        40  app2.rb:22

retained memory by class
-----------------------------------
        40  String

retained objects by gem
-----------------------------------
         1  other

retained objects by file
-----------------------------------
         1  app2.rb

retained objects by location
-----------------------------------
         1  app2.rb:22

retained objects by class
-----------------------------------
         1  String


Allocated String Report
-----------------------------------
         6  "this is a log\n"
         5  app2.rb:21
         1  app2.rb:22

         1  ""
         1  app2.rb:22

         1  "this is a log\nthis is a log\n"
         1  app2.rb:22

         1  "this is a log\nthis is a log\nthis is a log\n"
         1  app2.rb:22

         1  "this is a log\nthis is a log\nthis is a log\nthis is a log\n"
         1  app2.rb:22


Retained String Report
-----------------------------------
         1  ""
         1  app2.rb:22

70